Hi Mary
Yes I have used Kew military records for one ancestor (John Nixon) with great success ! I used a professional researcher to examine Royal Artillery records. Ended up with 90 pages worth !
The reference I made in this link is to another ancestor (Henry Nixon) who was not part of the UK military as such but who had contact with a person who was - Senior Sgt Dalton - who became the head of the mounted escort for several NSW Governors.... Sgt Dalton paid an immigration deposit in 1883 on behalf of Henry Nixon to bring his younger brother (George Nixon) out from Athlone Ireland.
Cheers
Robert